The present invention relates to fusing apparatus and methods.
As used in this disclosure, the term "fusing" refers to a technique for joining electrically-conductive elements of a workpiece in which a "fusing" electrode is contacted with one element adjacent the joint between the elements so that the fusing electrode forces the elements together. A "ground" electrode is also contacted with the workpiece, typically at a location remote from the joint, and electrical current is passed through the electrodes and workpiece. Heat generated by the electrical current, and the high pressure applied by the fusing electrode, causes a bond to form between the workpiece elements. The fusing electrode typically has higher resistivity than the workpiece elements, and ordinarily has a small contact surface region bearing on the workpiece. Thus, the major portion of the heat used in the process ordinarily is produced in the fusing electrode itself. Fusing techniques, also referred to as "hot staking" are used in a wide variety of industrial applications. For example, the windings and commutator bars of dynamoelectric machine rotors typically are joined to one another by fusing in mass production.
The productivity of fusing equipment and processes heretofore has been impaired by loss of productive time occasioned by electrode changes. As the electrodes are contacted with successive workpieces, the contact surfaces which engage the workpieces wear and deteriorate until the fusing action is impaired. Such wear and deterioration typically affect the fusing electrode more severely than the ground electrode, inasmuch as the fusing electrode ordinarily operates under more severe conditions of heat and load than the ground electrode. With the fusing equipment and methods utilized heretofore, the fusing process was interrupted whenever one or both of the electrodes became unacceptably worn. The fusing equipment remained idle for the time required to remove the worn electrode, replace it with a new electrode, and adjust the new electrode to the proper position in the equipment. Such interruptions in productivity of the fusing equipment have been particularly troublesome where the fusing process is integrated with other equipment in an automated production system, so tht interruptions in operation of the fusing apparatus can stop the entire production line. Also, wear and deterioration of the electrodes may cause unsatisfactory joining of the workpiece elements. Such defective joining can lead to waste of incoming parts, increased inspected and/or rework costs, and diminished outgoing product quality.
There have accordingly been needs heretofore for fusing equipment and methods which can provide continued, substantially uninterrupted productivity and consistent product quality despite electrode wear and deterioration. These needs have been particularly acute in fusing methods and apparatus for fusing the conductors and commutators of dynamoelectric machine rotors such as the rotors of small electric motors.